Power control circuit

ABSTRACT

A power control circuit is disclosed which may comprise a transformer having a primary winding and at least one secondary winding, a first and a second series circuit, and a rectifier circuit. The first series circuit may include a first DC power source, a first transistor and the primary winding of the transformer. The second series circuit may include the primary winding of the transformer, an excitation coil arranged to flow through the primary winding of the transformer a current which increases with time, a second DC power source and a second transistor. The rectifier circuit may be connected with the secondary winding of the transformer. In this power control circuit, an excitation current is first caused to flow through the primary winding of the transformer so that energy is stored therein. Thereafter, a current opposite to the excitation current is caused to flow through the primary winding of the transformer, and a current induced from the current flowing from the secondary winding to the primary winding of the transformer and a current resulting from the energy stored in the primary winding of the transformer are superimposed upon each other in the secondary winding of the transformer. Finally, a current resulting from the superimposition is rectified by the rectifier circuit, so that a continuous output is provided.

This invention relates to a power control circuit. It is an object of the present invention to provide a power control circuit based on an entirely new concept, which has an enhanced efficiency of controlled output power available from the output side to the input power supplied from a power source, or an improved power conversion efficiency, is capable of providing an output stabilized against fluctuations in the power source and load, is quick in response, is of light weight and is highly reliable. As will be appreciated from the following description, the present invention is most effectively usable with a wide variety of applications such for example as various power amplifiers, DC-AC power converters, stabilized DC power sources, stabilized AC power sources and so forth.

According to an aspect of the present invention, there is provided a power control circuit comprising a transformer having a primary winding and at least one secondary winding; a first series circuit including a first DC power source, a first transistor and the primary winding of the transformer; a second series circuit including the primary winding, an excitation coil arranged to flow through the primary winding a current which increases with time, a second DC power source and a second transistor; and a rectifier circuit connected with the secondary winding of the transformer, wherein an excitation current is first caused to flow through the primary winding of the transformer so that energy is stored therein; thereafter, a current opposite to the excitation current is caused to flow through the primary winding; a current induced from the current flowing from the secondary winding to the primary winding of the transformer and a current resulting from the stored energy are superimposed upon each other in the secondary winding of the transformer; and a current resulting from the superimposition is rectified by the rectifier circuit so that an output is provided.

Other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

FIG. 1 is a diagram showing a basic circuit arrangement according to the present invention.

FIG. 2 is a view illustrating various waveforms which occur in the circuit shown in FIG. 1.

FIG. 3 is a diagram showing another basic circuit arrangement according to the present invention.

FIG. 4 is a circuit diagram showing an embodiment of the present invention.

FIG. 5 is a view illustrating various waveforms which occur in the circuit of FIG. 4 when the circuit is in a steady state.

FIG. 6 is a view illustrating various waveforms which occur in the circuit of FIG. 4 when the circuit is in a transient state.

FIGS. 7 and 8 are views useful for explaining the operation of an applied form of the circuit shown in FIG. 4.

FIG. 9 is a circuit diagram showing a further embodiment of the present invention.

With reference to the drawings, the basic concept of the present invention will be described below. Referring first to FIG. 1, there is shown a basic circuit according to the present invention, which includes a transformer T₁ comprising a primary winding L₁ and a secondary winding L₂ ; a first series circuit including a DC power source E₁, a transistor Q₁ and the primary winding L₁ of the transformer T₁ ; and a second series circuit including a DC power source E₂, a transistor Q₂, the primary winding L₁ of the transformer T₁ an excitation coil L₃. The transformer T₁ has the secondary winding L₂ connected to a load R_(L) through a diode D₁.

Waveforms which occur at various points in the circuit of FIG. 1 are shown at (a), (b) and (c) in FIG. 2. Description will now be made of the operation of the circuit shown in FIG. 1.

Referring to FIG. 2(a), a base current i_(B1) is supplied to the transistor Q₁ at a point of time t_(A), whereby the transistor Q₁ is turned on so that an excitation current i₁ ' is passed through the primary winding L₁ of the transformer T₁. As a result, a voltage is induced across the secondary winding L₂ of the transformer T₁, but no secondary current i₂ is permitted to flow due to the fact that the induced voltage is of reverse polarity with respect to the diode D₁. The excitation current i₁ ' increases with time from zero in the negative direction, so that the magnetic flux φ which occurs in the core of the transformer T₁ is increased.

At a point of time t_(B), the base current i_(B1) of the transistor Q₁ is interrupted so that this transistor is turned off. At the same time, a base current i_(B2) is supplied to the transistor Q₂ so that this transistor is turned on. Thus, the excitation current i₁ ' flowing through the primary winding L₁ of the transformer T₁ is interrupted to be zero, while the primary current i₁ is permitted to flow therethrough. The primary current i₁ increases with time from zero due to the fact that the excitation coil L₃ is inductive. In this way, the energy stored in the transformer T₁ for the time t_(A) -t_(B) results in a flyback voltage being generated in the secondary winding L₂ at the point of time t_(B), whereby a secondary current i₂ is caused to flow so that the magnetic flux φ occurring in the core of the transformer T₁ becomes continuous.

At a point of time t_(C), the transistor Q₂ is turned off so that the primary current i₁ is interrupted to be zero. Referring to FIG. 2, there is shown a state that the energy in the transformer is zero. Energy is stored in the excitation coil L₃ by the primary current i₁.

During the time t_(B) -t_(C), the aforementioned secondary current i₂ decreases with time, as indicated by a hatched portion L₁ ' in FIG. 2(a). As the induced voltage occurring in the secondary winding L₂ is of forward polarity with respect to the diode D₁, the secondary current i₂ increases with time from zero as indicated by the hatched portion L₁ in FIG. 2(a). Thus, the secondary current i₂ flowing for the time t_(B) -t_(C) is caused to have a flat waveform which results from superimposition of the hatched portions L₁ ' and L₁ shown in FIG. 2(a).

For the convenience of explanation, it is assumed in FIG. 2(b) that there once again occurs the initial condition that no energy is stored in the transformer T₁ or excitation coil L₃. At a point of time t_(A) ', the transistor Q₁ is turned on so that an excitation current i₁ ' is caused to flow through the primary winding L₁ of the transformer T₁ in such a manner as to increase with time from zero in the negative direction. At a point of time t_(B) ', the transistor Q₁ is turned off while the transistor Q₂ is turned on, whereupon the aforementioned excitation current i₁ ' is interrupted to be zero while the primary current i₁ increases with time from zero as was the case with FIG. 2(a). By making the time t_(A) '-t_(B) ' longer than the time t_(A) -t_(B) shown in FIG. 2(a), a current which is higher than that which flowed at the point of time t_(B) in FIG. 2(a) is caused to flow through the primary winding L₁ at the point of time t_(B) ', so that the energy stored in the transformer T₁ is increased and the magnetic flux φ occurring in the core of the transformer T₁ is also increased. Furthermore, the secondary current i₂ is caused to flow through the secondary winding L₂ so that the aforementioned magnetic flux φ becomes continuous. By rendering the transistor Q₂ non-conductive at a point of time t_(C) ', the primary current i₁ is made to be zero. During the time t_(B) '-t_(D) ', the secondary current i₂ induced by the excitation current i₁ ' decreases with time as indicated by a hatched portion L₁ ' in FIG. 2(b). The secondary current i₂ resulting from the primary current i₁ increases with time as indicated by a hatched portion L₁ in FIG. 2(b), but at a point of time t_(C) ', this secondary current becomes nil. However, during the time t_(C) '-t_(D) ', energy remains stored in the transformer T₁ so that the secondary current i₂ induced by the excitation current i₁ ' decreases with time down to zero as is seen from the hatched portion L₁ ' in FIG. 2(b).

In this way, the secondary current i₂ which flows during the time t_(B) '-t_(C) ' can be made to have a flat waveform which results from superimposition of the hatched portions L₁ ' and L₁ in FIG. 2(b). And the secondary current i₂ rises up with a higher value at the point of time t_(B) ' than at the point of time t_(B).

At the point of time t_(C) ', the energy stored in the transformer T₁ is still present; thus, by making the design such that the transformer Q₁ is again turned on concurrently with turning-off of the transistor Q₂, it is possible to produce an operational current waveform such as occurs during the time t_(B) "-t_(D) " in FIG. 2(c).

At a point of time t_(A) ", the excitation current i₁ ' rises up with a value higher than zero and increases with time in the negative direction so that the negative residual flow φ occurring in the core of the transformer T₁ becomes continuous. Thus, by making the time t_(A) "-t_(B) " substantially equal to the time t_(A) -t_(B) in FIG. 2(a), and by making the design such that the transistor Q₂ is turned on concurrently with turning-off of the transistor Q₁, the excitation current i₁ ' is made to be zero after having reached a value lower than the current value at the point of time t_(b).

If energy remains in the excitation coil L₃ at the point of time t_(B) ", then the primary current is caused to rise up not from zero but from a value higher than zero and thus increases with time. Consequently, during the time t_(B) "-t_(C) ", the secondary current i₂ also rises up with a value higher than zero as indicated by a hatched portion L₁ in FIG. 2(c), and increases with time. At the point of time t_(C) ", the transistor Q₂ is turned off so that the primary current i₁ is made to be zero, and the hatched portion L₁ in FIG. 2(c) is also made to be zero.

For the time t_(C) "-t_(D) ", energy remains stored in the transformer T₁ ; thus, the secondary current i₂ such as indicated by a hatched portion L₁ ' in FIG. 2(c) is permitted to flow which decreases with time down to zero. In this way, the secondary current i₂ which flows during the time t_(B) "-t_(C) " can be made to have a flat waveform resulting from superimposition of the hatched portions L₁ ' and L₁ in FIG. 2(c). And the secondary current i₂ rises up with a higher value than that at the point of time t_(B) ' in FIG. 2(b).

As will be appreciated from the foregoing description, the secondary current i₂ available from the secondary winding L₂ of the transformer T₁ via the diode D₁ is proportional to the sum of the current resulting from the energy stored in the transformer T₁ and the rise-up current flowing through the primary winding L₁ of the transformer T₁. Thus, by controlling the energy stored in the transformer T₁ and the residual energy in the excitation coil L₃, it is possible to control the aforementioned secondary current i₂.

In this way, according to the present invention, the secondary current i₂ can be taken out with a waveform which is flat with respect to time and with a controlled value. It is required that the energy stored in the transformer T₁ be such that the magnetic flux φ occurring in the core of the transformer T₁ is lower than the saturation magnetic flux density. However, by virtue of the fact that the rise-up version of the primary current i₁ is added to the current resulting from the energy stored in the transformer T₁, the secondary current i₂ can be taken out as one which has higher energy than that obtained immediately before the saturation magnetic flux density is reached.

Though the basic circuit shown in FIG. 1 includes two DC power sources and two transistors, it is also possible to achieve operation similar to that illustrated in FIG. 2, by employing a single DC power source and four transistors as in the circuit shown in FIG. 3.

The arrangement of FIG. 3 comprises a first series circuit including a DC power source E_(B), a first transistor Q₁, the primary winding L₁ of transformer T₁ and a third transistor Q₃, and a second series circuit including the DC power source E_(B), a second transistor Q₂, the primary winding L₁ of the transformer T₁, an excitation coil L₃ and a fourth transistor Q₄, with the secondary winding L₂ of the transformer T₁ being coupled to a load R_(L) through a diode D₁.

With the arrangement mentioned above, the transistors Q₁ and Q₃ are turned on at the same time while the transistors Q₂ and Q₄ are turned off at the same time, so that a current is permitted to flow which corresponds to the excitation current i₁ ' shown in FIG. 1; and thereafter the transistors Q₂ and Q₄ are turned on at the same time while the transistors Q₁ and Q₃ are turned off at the same time, so that a current is permitted to flow which corresponds to the primary current i₁ shown in FIG. 1. In this way, the circuit of FIG. 3 can operate in a manner similar to that described above in connection with FIG. 2.

By providing a polarity reversing circuit comprising a single DC power source and four transistors, there can be provided a power control circuit similar to that shown in FIG. 1. Such a circuit arrangement is advantageous in that only one power source is needed.

Referring now to FIG. 4, there is shown an embodiment of the present invention, which will be described in detail below.

The circuit arrangement shown in FIG. 4 includes a transformer T₁₁ comprising a primary winding L₁₁ and a secondary winding L₁₂ ; a second transformer T₂₁ comprising a primary winding L₂₁ and secondary winding L₂₂ ; DC power sources E₁₁ and E₂₁ ; transistors Q₁₁ and Q₂₁ ; diodes D₁₁ and D₂₁ ; and a load R_(L).

In the circuit arrangement of FIG. 4, there are provided two series circuits: one including the DC power source E₁₁, transistor Q₁₁, the primary winding L₂₁ of the transformer T₂₁ and the primary winding L₁₁ of the transformer T₁₁, and the other including the DC power source E₂₁, transistor Q₂₁, the primary winding L₂₁ of the transformer T₂₁ and the primary winding L₁₁ of the transformer T₁₁. The secondary windings L₁₂ and L₂₂ of the two transformers are connected in parallel with each other so that rectified outputs of the same polarity can be obtained from these secondary windings L₁₂ and L₂₂ through the diodes D₁₁ and D₂₁ respectively, by alternately turning on and off the transistors Q₁₁ and Q₂₁. Generically, according to the embodiment shown in FIG. 4, there is provided a power control circuit which comprises a first and a second transformer each having a primary winding and at least one secondary winding; a first series circuit including a first DC power source, a first transistor and the primary windings of the first and second transformers; a second series circuit including a second DC power source, a second transistor and the primary windings of the first and second transformers; and rectifier circuits connected in parallel with each other so that rectified outputs available from the secondary windings of the first and second transformers respectively are of the same polarity, wherein the first and second transistors are alternately turned on and off so that negative and positive currents are caused to flow through the primary windings of the two transformers; after energy has been stored in the primary winding of one of the transformers, a current which increases with time is caused to alternately flow through the respective primary windings; a current induced from the current flowing from each of the secondary windings to one of the primary windings is superimposed upon a current which results from energy stored in the other primary winding; and the current resulting from the superimposition is rectified by the aforementioned rectifier circuits so that there is provided a continuous output.

Operational current waveforms occurring at various points in the circuit shown in FIG. 4 are illustrated in FIG. 5.

At a point of time t₀, a base current i_(B11) is supplied to the transistor Q₁₁ so that this transistor Q₁₁ is turned on, while at the same time the base current i_(B21) of the transistor Q₂₁ is interrupted so that the transistor Q₂₁ is turned off. Assuming that energy remains stored in the transformer T₂₁, the primary current i₁₁ is caused to rise up with a predetermined negative value and increases with time in the negative direction. Furthermore, assuming that a predetermined quantity of energy is stored in the transformer T₁₁, a secondary current i₁₂ which is caused to flow from the secondary winding L₁₂ of the transformer T₁₁ is combined with a current resulting from the voltage induced from the primary winding so that the secondary current i₁₂ is caused to have a flat waveform as shown in FIG. 5 in which each hatched portion indicates the energy stored in the transformer T₁₁.

At a point of time t₁, energy remains stored in the transformer T₁₁. At this point, the base current i_(B11) of the transistor Q₁₁ is interrupted so that the transistor Q₁₁ is turned off, while at the same time a base current i_(B21) is supplied to the transistor Q₂₁ so that the latter is turned on, as a result of which the primary current i₁₁ is made to be zero, so that the secondary current i₁₂ also becomes zero. The primary current i₂₁ rises up with a predetermined value and increases with time so that the magnetic flux φ occurring in the core of the transformer T₁₁ becomes continuous. Since energy resulting from the primary current i₁₁ is stored in the other transformer T₂₁, the secondary current i₂₂ which flows from the secondary winding L₂₂ of the other transformer T₂₁ through the diode D₂₁ is combined with a current resulting from the voltage induced from the primary winding L₂₁, as a result of which the secondary current i₂₂ is caused to have a flat waveform as shown in FIG. 4, in which each hatched portion indicates the energy stored in the other transformer T₂₁. In this way, a current i_(S) which results from the combination of the aforementioned secondary currents i₁₂ and i₂₂ is applied to the load R_(L) as a continuous DC current.

At the point of time t₂, energy remains stored in the transformer T₁₁ ; thus, by interrupting the base current i_(B21) of the transistor Q₂₁ to turn off this transistor while at the same time supplying a base current i_(B11) to the transistor Q₁₁ to turn on this transistor, the primary current i₂₁ is made to be zero so that the secondary current i₂₂ is also made to be zero.

Through repetition of the aforementioned operation with the time t₀ -t₂ as one cyclic period T, continuous DC current i_(S) can be supplied to the load R_(L), thus resulting in a flat DC voltage e_(O). In this case, composite primary currents i_(p) flowing from the DC power sources E₁₁ and E₂₁ appear as positive-going and negative-going waves, as shown in FIG. 5.

In the foregoing explanation, description has been made of the case where the inductance of the primary winding L₁₁ of the transformer T₁₁ is equal to the inductance of the primary winding L₂₁ of the transformer T₂₁ and the circuit operation is in a steady state. Description will now be made of the case where the circuit operation is in a transient state.

The circuit operation will be described below with reference to FIG. 6 which shows the operating current and voltage waveforms occurring at the various points in the circuit of FIG. 4.

At a point of time t₁₀, no energy is stored in the transformer T₁₁ or T₁₂ ; thus, by supplying base current i_(B11) to the transistor Q₁₁ to render this transistor conductive, the primary current i₁₁ is increased from zero and the composite current i_(S) is also increased from zero, so that the output voltage e_(O) available across the terminals of the load R_(L) is also increased from zero. In this way, energy is progressively stored in the transformer T₂₁, but excitation current is also caused to flow through the primary winding L₁₁ so that reverse energy which cannot be taken at the load R_(L) is stored therein. This is because no energy is as yet stored in the transformer T₁₁ and therefore the excitation current flowing through the primary winding L₁₁ cannot be cancelled. However, energy stored in the transformer T₁₁ is much less than that stored in the transformer T₂₁, since the output voltage e_(O) is still very low and hence the voltage applied to the primary winding L₁₁ is also still very low so that the voltage from the DC power source E₁₁ is mostly applied to the primary winding L₂₁.

At a point of time t₁₁, the base current i_(B11) of the transistor Q₁₁ is interrupted so that this transistor Q₁₁ is turned off, and at the same time, a base current i_(B21) is supplied to the transistor Q₂₁ so that the latter transistor Q₂₁ is turned on. The energy stored in the primary winding L₂₁ is dissipated as secondary current i₂₂, but as the reverse energy which cannot be taken at the load R_(L) is stored in the primary winding L₁₁, a reverse voltage is induced in the primary winding L₁₁, whereby the primary current i₂₁ is prevented from flowing through the transistor Q₂₁. At the point of time t₁₁, the transistor Q₂₁ is in such a state that this transistor is ready to be turned on, but no collector current is permitted to flow therethrough.

At a point of time t₁₂, energy is stored in the transformer T₁₁ and energy remains stored in the other transformer T₂₁ ; thus, by again turning on the transistor Q₁₁ while at the same time turning off the transistor Q₂₁, the primary current i₁₁ is caused to rise up with a high value so that the output voltage e_(O) further builds up.

Assuming that the windings of the transformers T₁₁ and T₂₁ have an equal number of turns, the output voltage e_(O) which is obtained by alternately turning on and off the transistors Q₁₁ and Q₂₁ with time t₁₀ -t₁₂ as one cyclic period T is given as follows: ##EQU1##

As is seen from the above equation (1), the output voltage e_(O) exponentially continuously builds up irrespective of the cyclic period T. The primary composite current i_(p) takes a pulsating saw-tooth waveform consisting of alternate positive-going and negative-going portions, and the cyclic period of such saw-tooth waveform depends on the aforementioned cyclic period; thus, the shorter the cyclic period T, the lower becomes the amplitude of the saw-tooth waveform.

As is seen from the operating current and voltage waveforms shown in FIG. 6, the primary current i₁₁ of the transistor Q₁₁ and the primary current i₁₂ of the transistor Q₂₁ differ from each other in respect of amplitude, but the cyclic period of the saw-tooth waveform is equal to the cyclic period with which the transistors Q₁₁ and Q₂₁ are turned on and off. This is because the residual energy in the transformers T₁₁ and T₂₁ is non-uniform. By adjusting the timing for turning-on and off of the transistors Q₁₁ and Q₂₁, the amplitudes of the primary currents i₁₁ and i₂₁ are equalized as is the case with the waveform i_(p) shown in FIG. 5. Thus, the cyclic period of the saw-tooth waveform can be made as short as T/2. Furthermore, as is apparent from the above equation (1), the output voltage e_(O) reaches E_(B) /2 γ, where E_(B) =|E₁ |=|E₂ |, so that a steady state or a steady-state value is realized, but the lower the transient value of the output voltage e_(O) relative to the steady-state value of the output voltage e_(O), the more sharply rises up the saw-tooth waveform. At a point of time t₁₃, the transistors Q₁₁ and Q₂₁ are rendered non-conductive at the same time, so that energy flowing out of the transformers T₁₁ and T₂₁ results in the secondary current i₁₂ and i₂₂ flowing simultaneously; as a result, the output voltage e_(O) is given as follows:

    e.sub.O =e.sub.O (O)·e.sup.-αt              (2)

where e_(O) (O) indicates the amplitude of the output voltage e_(O) when the transistors Q₁₁ and Q₂₁ are turned off at the same and which exponentially continuously decreases. The output voltage is continuous even when it is changed from increasing to decreasing.

Through the operation illustrated by the operating waveforms in FIG. 6, the circuit of FIG. 4 is enabled to function as a DC-DC converter which is arranged to convert input voltages provided by the DC power sources E₁₁ and E₂₁ into different DC voltages. Furthermore, by suitably selecting the circuit constants, it is possible to determine the rise and fall time constants of the output voltage e_(O) as desired. Still furthermore, according to the present invention, it is possible to obtain an output voltage e_(O) which is continuous and ripple-free.

Other waveforms which occur in the circuit of FIG. 4 are shown in FIG. 7, and description will now be made of means for controlling the output voltage e_(O).

In FIG. 7, t₂₀ denotes a point of time slightly prior to the point of time when the output voltage e_(O) reaches a steady-state value. At the point of time t₂₀, the transistor Q₁₁ is turned on, while at the same time the transistor Q₂₁ is turned off; thus, the output voltage e_(O) builds up with time so as to finally reach the steady-state value. At a point of time t_(21a), the transistors Q₁₁ and Q₂₁ are turned off at the same time, and as a result, the output voltage e_(O) begins decreasing. At a point of time t_(21b) when the output voltage e_(O) assumes the same value as that at the point of time t₂₀, the transistor Q₂₁ is turned on while at the same time the transistor Q₁₁ is turned off; thus, the output voltage e_(O) builds up again. Further, at a point of time t_(22a) when the output voltage e_(O) assumes the same value as that at the point of time t_(21a), the transistors Q₁₁ and Q₂₁ are turned off at the same time, and as a result, the output voltage e_(O) again beings decreasing. At a point of time t_(22b) when the output voltage assumes the same value as that at the point of time t₂₀, again, the transistor Q₁₁ is turned on while at the same time the transistor Q₂₁ is turned off. Thus, the output voltage e_(O) builds up again.

Repetition of the foregoing operation with the time t₂₀ -t_(22b) as one cyclic period T results in the output voltage e_(O) having small triangular ripples and being maintained at a value lower than the steady-state value.

At a point of time t₂₃, the transistors Q₁₁ and Q₂₁ are both turned off, and operated for a time longer than the aforementioned time t_(21a) -t_(21b) ; thus, the output voltage e_(O) decreases to be lower than the value at the point of time t₂₀. At a point of time t₂₀ ', again, the transistor Q₁₁ is turned on while at the same time the transistor Q₂₁ is turned off, and as a result, the output voltage e_(O) builds up. At a point of time t_(21a) ' when the output voltage e_(O) has built up a little, the transistors Q₁₁ and Q₂₁ are both turned off, and as a result the output voltage e_(O) begins decreasing. At a point of time t_(21b) ' when the output voltage e_(O) assumes a value equal to that at the point of time t₂₀ ', the transistor Q₂₁ is turned on while at the same time the transistor Q₁₁ is turned off, and thus the output voltage e_(O) again begins increasing. Further, at a point of time t_(22a) ' when the output voltage e_(O) has a value equal to that at the point of time t_(21a) ', the transistors Q₁₁ and Q₂₁ are both turned off, and thus the output voltage e_(O) decreases. At a point of time t_(22b) ' when the output voltage e_(O) assumes a value equal to that the point of time t₂₀ ', the transistor Q₁₁ is turned on while at the same time the transistor Q₂₁ is turned off, and thus the output voltage e_(O) builds up.

In this way, repetition of the operation mentioned just above with the time t₂₀ '-t_(22b) ' as one cyclic period T results in the output voltage e_(O) having small triangular ripples and being maintained at a value lower than that during the aforementioned time t₂₀ -t₂₃.

The current i_(p) available from the DC power sources E₁₁ and E₂₁ rises up with a negative value at the point of time t₂₀ ; it increases with time in the negative direction; it reaches a negative maximum value at the point of time t_(21a) ; and thereafter it becomes zero. At the point of time t_(21b), the current i_(p) rises up with a positive value which is equal in absolute value to the value at the point of time t₂₀ ; it increases with time; it reaches a positive maximum value which is equal in absolute value to the value at the point of time t_(21a) ; and thereafter it becomes zero. At the point of time t_(22b), the current i_(p) rises up with a negative value which is equal in absolute value to the value at the point of time t₂₀, and it increases with time.

Through repetition of the foregoing operation, the current i_(p) from the DC power sources E₁₁ and E₂₁ reaches, at the point of time t₂₃, a positive maximum value which is equal in absolute value to the value at the point of time t_(22a) ; and thereafter it becomes zero.

At the point of time t₂₀ ', the current i_(p) rises up with a negative value which is lower in absolute value than the value at the point of time t₂₀ ; it increases with time; at the point of time t_(21a) ', it reaches a negative maximum value which is lower in absolute value than the value at the point of time t_(21a) ; and thereafter it becomes zero. At the point of time t_(21b) ', the current i_(p) rises up with a negative value which is equal in absolute value to the value at the point of time t₂₀ '; it increases with time in the negative direction; at the point of time t_(22a) ', it reaches a negative maximum value which is equal in absolute value to the value at the point of time t_(21a) '; and thereafter it becomes zero. At the point of time t_(22b) ', the current i_(p) rises up with a negative value which is equal in absolute value to the value at the point of time t₂₀ ', and it increases with time in the negative direction.

Thus, repetition of the foregoing operation results in the current i_(p) from the DC power sources E₁₁ and E₂₁ having such a waveform as shown in FIG. 6.

As will be seen from FIG. 7, during the time when the output voltage e_(O) is high, the current i_(p) from the DC power sources E₁₁ and E₂₁ rises up with a high value, and the ratio of the period of time during which the current i_(p) is flowing to the period of time during which the current i_(p) is interrupted, is low. During the time when the output voltage e_(O) is low, the current i_(p) rises up with a lower value than that with which it rises up during the time when the output voltage e_(O) is higher, and the ratio of the period of time during which the current i_(p) is flowing to the period of time during which the current i_(p) is interrupted, is high. Thus, the output voltage e_(O) is continuous despite the discontinuity of the current i_(p) from the DC power source E₁₁ and E₂₁.

As will be appreciated from the above explanation, it is possible to maintain the output voltage e_(O) at any desired value lower than the steady-state value by inserting the time when the transistors Q₁₁ and Q₂₁ are both rendered non-conductive between the times when the transistors Q₁₁ and Q₂₁ are alternately rendered conductive and non-conductive, and by changing the ratio of the period of time during which one of the transistors Q₁₁ and Q₂₁ is conducting to the period of time during which the transistors Q₁₁ and Q₂₁ are both non-conducting.

The output voltage e_(O) can also be changed continuously, and the control response thereof is shown in FIG. 8, from which it will be seen that the output voltage e_(O) can be approximated by a sequence of triangular waves of a low amplitude. Thus, the circuit according to the present invention is also responsive to a waveform of the output voltage e_(O) which has lower rise and fall speeds than those shown in FIG. 5.

A further embodiment of this invention is shown in FIG. 9, which will now be explained. FIG. 9 is basically similar to FIG. 4, and therefore parts of FIG. 9 corresponding to those of FIG. 4 are indicated by like references.

The circuit of FIG. 9 includes input terminals 1a, 1b and 1c connected with DC power sources E₁₁ and E₂₁, output terminals 2a and 2b, a differential amplifier 3, a base current control circuit 4, input terminal 5 of the differential amplifier 3 to which is applied a control voltage V_(c), voltage dividing resistors R₁ and R₂. The present power control circuit is generally shown at 6. Diodes D₁₃ and D₁₄ connected in parallel with transistors Q₁₁ and Q₂₁ are provided for the purpose of permitting of reverse current flow, as described in connection with FIG. 6.

Energy stored in the primary winding L₁₁ provides a reverse voltage induced therein, and energy stored in the primary winding L₂₁ also provides a reverse voltage induced therein. The optimum condition for the circuit operation is such that the sum of the reverse voltages induced in the primary windings L₁₁ and L₂₁ is equal to the voltage derived from each of the DC power sources E₁₁ and E₂₁, and such a condition is satisfied in the example of FIG. 8 since the waveform shown therein is clamped by the power source voltage.

In this way, the reverse voltages are retrieved by the DC power sources E₁₁ and E₂₁ as excess energy without being wasted, through a closed circuit including the DC power source E₁₁, diode D₁₃ and primary windings L₂₁ and L₁₁ and through a closed circuit including the diode D₁₄, DC power source E₂₁ and primary windings L₁₁ and L₂₁.

The diodes D₁₃ and D₁₄ also serve to achieve retrieval to the DC power sources E₁₁ and E₂₁ of spike voltages which tend to be induced in the primary windings due to the leakage inductance between the primary and the secondary winding of each transformer.

With the conventional switching power sources, it has been necessary to separately provide a spike absorbing winding in the transformers in order to make possible retrieval to the DC power source of spike voltages tending to occur when flyback voltage rises up.

In contrast thereto, according to the present invention, the necessity of providing a separate spike-absorbing winding in the transformers is eliminated; spike voltages occurring in the primary windings are clamped by the power source voltage and can be retrieved as excess energy by the DC power sources; the circuit arrangement is simplified; and the transistors Q₁₁ and Q₂₁ can be prevented from breakage due to over-voltage.

The embodiment shown in FIG. 9 is similar to the embodiment shown in FIG. 4, except that a feedback circuit is additionally provided. According to this embodiment, there is provided a power control circuit wherein a continuous triangular wave voltage obtained across the output terminals 2a and 2b and the input control voltage V_(c) are compared in the differential amplifier 3; the times when the transistors Q₁₁ and Q₂₁ are rendered conductive and non-conductive, are controlled in accordance with the resultant differential output; and thus a homologous rectangular wave voltage proportional to the aforementioned input control voltage V_(c) is obtained across the load R_(L).

When a positive control voltage V_(c) is applied to the input terminals 5, output voltage e_(O) available between the output terminals 2a and 2b and the positive control voltage V_(c) are compared and amplified in the differential amplifier 3; and the resultant differential output is supplied to the base current control circuit 4. This circuit 4 is arranged to control the times when the transistors Q₂₁ and Q₁₁ are alternately rendered conductive and non-conductive and the times when the transistors Q₂₁ and Q₁₁ are rendered non-conductive at the same time, so that the output voltage e_(O) available across the output terminals 2a and 2b becomes proportional to the positive control voltage V_(c). In turn, the output voltage e_(O), which is proportional to the positive control voltage V_(c), is attenuated to e_(O) R₂ /(R₁ +R₂) by the dividing resistors R₁ and R₂, and then applied to another input terminal of the differential amplifier 3, whereby there is provided negative feedback. Thus, the output voltage e_(O), which is homologous to the control voltage V_(c), is given by the following expression:

    e.sub.O ≈R.sub.1 +R.sub.2 /R.sub.1 ·V.sub.c (3)

A capacitor C₁ may be inserted when it is required that small triangular ripples as well as small spikes tending to occur when switching of the transistors Q₁₁ and Q₂₁ is effected, be eliminated. The value for this capacitor does not have to be so high.

The circuit arrangement according to the embodiment shown in FIG. 9 can most commonly be employed for a stabilized DC power source device. With this arrangement, it is possible to make the output voltage e_(O) invariable or variable by employing a reference voltage source which provides an invariable or variable control voltage V_(c). The stabilized DC power source device embodying the present invention requires no complex smoothing circuit components at the output stage thereof unlike the conventional switching power sources. In the device embodying the present invention, it is only required that capacitor C₁ of low capacitance be inserted when needed; thus, a very quick control response, which substantially compares with that of a series-dropper type linear circuit power source, can be achieved, although it depends on the switching speed of the transistors Q₁₁ and Q₂₁. The current flowing through each portion of the circuit remains substantially unchanged with time, and this facilitates selection of the circuit elements and reduces power loss. Furthermore, as mentioned above, the number of turns of each transformer winding may be small, and yet an output above that achieved at the saturation magnetic flux density can be taken out, so that the core loss is relatively small; thus, the entire loss of the transformer can be reduced. In addition, the transformer per se can be miniaturized and made to be of light weight. Furthermore, since no smoothing circuit is needed as mentioned above, there occurs neither loss due to the presence of a smoothing choke nor loss due to a large current flowing in and out of a smoothing capacitor. In this way, according to the present invention, there is provided a switching power source with a greatly reduced loss and hence with an improved power efficiency.

The circuit according to the present invention is advantageous in that peak values of the currents flowing through the various portions thereof are lower than those in the conventional switching power source devices capable of providing substantially the same amount of power as that which is provided by the present circuit, and in that spike currents can be effectively retrieved by the DC power source so that spike noise can be minimized. Thus, according to the present invention, there is provided a switching power source circuit which is of light weight, of high performance, of high reliability and inexpensive.

Though, in the foregoing explanation, description has been made of the case where each transformer has a single secondary winding, it is also possible that each transformer may include a plurality of secondary windings so that output voltages can be separately taken out in a stabilized form.

In order to isolate, DC-wise, the DC power source and the output circuit from each other, coupling means such for example as photo-coupler may be provided in the amplification and control system of the differential amplifier 3 and base current control circuit 4, and by so doing, it is possible to realize, with ease, an output-input isolated type switching power source circuit.

The present invention is equally applicable where the control voltage V_(c) is AC, and in such a case, there is obtained an output voltage e_(O) homologous to the control voltage V_(c), so that a power control circuit responsive to a wide range of input power from DC to high frequency AC power can be realized.

As will be appreciated from the above description, the present invention finds extensive use in a wide range of applications such as in common power amplifiers, servo-amplifiers, DC-AC power converters, AC-AC power converters, constant AC voltage power sources, stabilized DC voltage sources the output voltage of which can be continuously changed from positive to negative, and so forth.

In the conventional power amplifiers, active elements such as transistors or the like have been used to constitute a linear circuit so that loss inevitably occurs in such elements, whereas in the present invention, such active elements are simply made to perform switching function so that loss tending to occur therein can be minimized. Furthermore, as described above in connection with FIG. 9, the circuit according to the present invention is greatly improved in respect of power conversion efficiency over the conventional power amplifiers. Still furthermore, according to the present invention, there is no need to specially provide a DC power source using a power transformer for power amplifier; rather, according to the present invention, DC power resulting from direct rectification of the commercial line power source can be utilized, and yet the signal output and input terminals can easily be isolated from the commercial line. In this way, according to this invention, there is provided a power amplifier which is inexpensive and of light weight. Thus, by applying the present invention to the aforementioned various applications, it is possible to realize devices which are of high efficiency, of high performance, of light weight, of high reliability and inexpensive.

Although this invention has been described with respect to some specific embodiments, it is to be understood that the invention is not restricted thereto but covers any and all modifications and changes which may be made within the scope of the appended claims. 

What is claimed is:
 1. A power control circuit comprising a transformer having a primary winding and at least one secondary winding; a first series circuit including a first DC power source, a first transistor and the primary winding of said transformer; a second series circuit including said primary winding, an excitation coil arranged to flow through said primary winding a current which increases with time, a second DC power source and a second transistor; and a rectifier circuit connected with the secondary winding of said transformer, wherein an excitation current is first caused to flow through the primary winding of said transformer so that energy is stored therein; thereafter, a current opposite to said excitation current is caused to flow through said primary winding; a current which is induced in the secondary winding by the current flowing through the primary winding of said transformer and a current resulting from the stored energy are superimposed upon each other in said secondary winding; and a current resulting from the superimposition is rectified by said rectifier circuit so that an output is provided.
 2. A power control circuit comprising a transformer having a primary winding and at least one secondary winding; a first series circuit including a DC power source, a first transistor, the primary winding of the transformer and a third transistor; a second series circuit including said DC power source, a second transistor, the primary winding of the transformer, an excitation coil arranged to flow through said primary winding a current which increases with time and a fourth transistor; and a rectifier circuit connected with the secondary winding of the transformer, wherein an excitation current is first caused to flow through the primary winding of the transformer so that energy is stored therein; thereafter, a current opposite to said excitation current is caused to flow through said primary winding; a current which is induced in the secondary winding by the current flowing through the primary winding of the transformer and a current resulting from the stored energy are superimposed upon each other in said secondary winding; and a current resulting from the superimposition is rectified by said rectifier circuit so than an output is provided.
 3. A power control circuit comprising a first and a second transformer each having a primary winding and at least one secondary winding; a first DC power source; a first series circuit including a first DC power source, a first transistor and the primary windings of the first and second transformers, a second series circuit including a second DC power source, a second transistor and the primary windings of the first and second transformers; and rectifier circuits connected in parallel with each other so that rectified output available from the secondary windings of the first and second transformers respectively are of the same polarity, wherein the first and second transistors are alternately turned on and off; so that positive and negative currents which increase with time are caused to alternately flow through the primary windings of said two transformers in such a manner that energy is stored in one of the transformers and a current which is induced in the secondary winding of the other transformer by the current flowing through the primary winding of said other transformer, is superimposed upon a current resulting from the energy stored in said other transformer after energy has been stored in the primary winding of one of the transformers, a current which increases with time is caused to alternately flow through the respective primary windings; a current which is induced in each of the secondary windings by the current flowing through one of the primary windings and a current resulting from the energy stored in the other primary winding are superimposed upon each other; and a current resulting from the superimposition is rectified by the rectifier circuits so that a continuous output is provided.
 4. A power control circuit according to claim 3, wherein between the times for which a positive and a reverse current are caused to flow through the primary windings of the first and second transformers, a time for which no such current are caused to flow therethrough, is inserted; and the ratio of the period of time during which said two currents are flowing to the period of time during which said two currents are not flowing, is varied, thereby controlling the output voltage.
 5. A power control circuit according to claim 3, wherein diodes are connected with the first and second transistors in reverse polarity with respect thereto. 